JPH05232835A - Fixing unit for electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent a sheet from being soiled with a toner mass stuck on the surface of a fixing roller by eliminating a gap between a thermister and a heating roller so that the direction of force which the thermister receives from the heating roller based on frictional force due to the rotation of the heating roller, passes through the supporting point position of a holding bracket and an angular moment is not actuated to the holding bracket, and to prevent the occurrence of the gap between a rotary heating roller and the thermister pressed thereon, at the time of fixing an image, as well. CONSTITUTION:A fixing bracket 36 is mounted on a top cover 35 covering the upper part of the heating roller 30. The holding bracket 37 is provided by supporting it by the fixing bracket 36, and simultaneously, pressed by a pressing member 42 to turn the holding bracket 37 by using a bearing part 37b as a supporting point, and the thermister 40 held on the tip is pressed on the heating roller 30. On the tangent B of the heating roller 30 at a pressing position A of the thermister 40, the bearing part 37b as the turnable supporting point of the holding bracket 37 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system using a laser, such as a printer, a copying machine, a facsimile, etc. (a system for transferring an image formed on a photoconductor to a sheet such as paper or envelope for recording). Therefore, the present invention can be applied to an electrophotographic apparatus that records on a sheet. More specifically, the present invention relates to a fixing device for fixing the transferred image on the sheet by passing heat and pressure between the sheet after the image transfer and applying heat and pressure in the electrophotographic apparatus.

[0002]

2. Description of the Related Art Conventionally, in this type of fixing device, as shown in FIGS. 4 and 5, for example, a fixing bracket 3 is attached to an upper cover 2 covering a heating roller 1, and the fixing bracket 3 is used. The holding bracket 4 is rotatably supported around a fulcrum 4a, and the holding bracket 4 is urged by an urging member 5 to rotate about the fulcrum 4a, and the thermistor 6 held at the tip thereof is heated. There is a configuration in which it is pressed against the roller 1.

However, when fixing an image, the thermistor 6 is used.
Then, the surface temperature of the heating roller 1 is detected, and the temperature of the heating roller 1 is controlled by the control means (not shown) based on the detection signal.

[0004]

However, in the conventional fixing device, when the heating roller 1 rotates in the direction shown by the arrow in FIG. 4 at the time of fixing an image, the thermistor 6 is generated based on the frictional force.
However, as shown in FIG. 6, at the pressing position a, the force of F indicated by the arrow in the tangential direction of the heating roller 1 is received. That power F
Is divided into a line connecting the fulcrum 4a of the holding bracket 4 and the pushing position a of the thermistor 6 and a direction perpendicular to the line, the component forces thereof are F ₁ and F _{2 as} shown in the figure.
Becomes Therefore, when the distance between the fulcrum 4a and the pushing position B is a, a moment of F ₂ × a is applied to the holding bracket 4 to weaken the urging force of the urging member 5. Therefore, there is a problem that the thermistor 6 is slightly lifted from the heating roller 1 and a slight gap is generated between the thermistor 6 and the heating roller 1.

When the image is fixed, the offset toner adhered to the surface of the heating roller 1 accumulates in the gap, and when the fixing device is stopped, the offset toner is solidified and sticks on the heating roller 1. The toner adheres to the surface. Form lump 7. Then, when the fixing device was driven again and the sheet was fixed by the heating roller 1, the sheet was rubbed with the toner lump 7 and stained.

Therefore, an object of the present invention is to fix an image at the time of image fixing.
It is to prevent a gap from being generated between the rotating heating roller and the thermistor pressed against it.

[0007]

Therefore, the present invention provides
For example, as shown in the following illustrated embodiment, the thermistor 40 is held by a holding bracket 37 and is biased by a biasing member 42 such as a coil spring to hold the holding bracket 37.
Is rotated about a fulcrum such as the protrusion 37b, and the thermistor 40 is pressed against the heating roller 30 to detect the surface temperature thereof.
The heating roll at the pressing position a of the thermistor 40.
It is characterized in that a fulcrum of the holding bracket 37 is provided on the tangent line B of the la 30.

[0008]

In the present invention, the thermistor 40 is heated by the rotation of the heating roller 30 due to frictional force.
The direction of the force received from passes through the fulcrum position of the holding bracket 37.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows an overall schematic structure of an internal mechanism in a laser printer including a fixing device which is an embodiment of the present invention.

Reference numeral 10 in the figure denotes the apparatus main body. The apparatus main body 10 is provided with a photoconductor 11 substantially in the center thereof, and a charger 12, an optical writer 13, a developing device 14, a transfer device 15, and a cleaning device 16 are sequentially arranged around the photoconductor 11. Then, as the photoconductor 11 rotates in the clockwise direction in the figure, the surface of the photoconductor 11 is uniformly charged by the charger 12, and then laser light is irradiated by the optical writer 13 to form an electrostatic latent image. The developing device 14 attaches toner to form a visible image. A paper feed cassette 18 is detachably attached to the right side of the apparatus body 10 in the figure. Then, the sheet S stored in the paper feed cassette 18 is fed out by rotating the paper feed roller 20 and abutted against the pair of registration rollers 21 to be stopped. After that, the registration roller 21 is rotated in synchronization with the rotation of the photoconductor 11 to convey the sheet S, and the transfer device 15 transfers the visible image on the surface of the photoconductor 11 to the sheet S. After the image transfer, the sheet S is conveyed to the fixing device 23 according to the present invention, and the transferred image on the sheet S is fixed there. After the image is fixed, the sheet S is ejected onto the sheet ejection path 2
Then, the sheet is discharged to the sheet discharge section 25 through 4. On the other hand, the surface of the photoconductor 11 after the image transfer is cleaned by the cleaning device 16.

By the way, the above-mentioned fixing device 23 is provided with a heating roller 30 having a heater 29 built therein and a pressure roller 31 which is pressed against the heating roller 30, and these heating roller 30 and pressure roller are provided.
The sheet S is put between the rollers 31, and heat and pressure are applied there to fix the sheet.

The fixing device 23 is constructed in more detail as shown in FIGS. 1 and 2. Reference numeral 3 in the figure
Reference numeral 5 denotes an upper cover that covers the upper portion of the heating roller 30. An inclined portion 35a is provided downward to the right in the figure, and a window hole 3 is provided therein.
Open 5b. On the upper cover 35, the inclined portion 3
A fixing bracket 36 is attached near 5a. The fixing bracket 36 is plate-shaped, and has both ends thereof on the left side in the drawing on the base end side so as to wind up both ends upward from the base end side to the tip end side to provide a bearing portion 36a, and at the center of the tip end side, an upper spring receiving member. Piece 36
b is projected, and the hooking portion 36c is cut and raised downward at the tip.

The holding bracket 37 is supported by the fixed bracket 36 described above. The holding bracket 37 is
A window hole 37a is opened at approximately the center, and both ends of the base end side on the left side of the drawing are cut out to form protrusions 37b at both ends, while the tip side is bent at two bending portions 37c and 37d in the middle, and the tip end side is bent. The lower spring receiving piece 37e is cut and raised upward. A thermistor mounting plate 38 is provided on the lower surface at the tip of the holding bracket 37. The thermistor mounting plate 38 is covered with a thermistor 40 on its lower surface to attach foamed silicon 39, and the resin tape 4 is attached to the outer periphery of the foamed silicon 39.
1 is attached to cover the thermistor 40.

Then, the protrusion 37b is connected to the bearing portion 36.
The shaft spring 37b is rotatably provided with the shaft portion 37b as a fulcrum, and the upper spring receiving piece 36 is inserted through the window hole 37a.
b is projected slightly upward and is arranged so as to face the lower spring receiving piece 37e. In the figure, 37f is the lower spring receiving piece 37.
It is a hooking portion provided on e.

On the other hand, the upper spring receiving piece 36b of the fixing bracket 36 and the lower spring receiving piece 37e of the holding bracket 37.
A biasing member 42 such as a coil spring is provided in between, and the hook portions 36c and 37f are inserted into the upper and lower ends thereof.

Then, the holding bracket 37 is urged by the urging member 42 to rotate the holding bracket 37 with the protrusion 37b as a fulcrum, and the thermistor 40 is pressed against the heating roller 30 through the window hole 35b. Become.

In the present invention, as shown in FIG.
The heating roll at the pressing position a of the thermistor 40.
The rotation fulcrum (shaft portion 37b) of the holding bracket 37 is provided substantially on the tangent line B of the la 30.

However, when the heating roller 30 is rotated in the clockwise direction indicated by the arrow at the time of fixing the image, the thermistor 40 is heated by the heating roller 3 at the pressing position B based on the frictional force.
Although the force F is applied in the tangential direction of 0, the thermistor 40 is heated by the rotation of the heating roller 30 due to the frictional force.
The direction of the force received from passes through the fulcrum position of the holding bracket 37. Therefore, the urging force of the urging member 42 is not weakened, the thermistor 40 does not float, and the thermistor 40 is constantly pressed against the heating roller 30 with an appropriate urging force. And the thermistor 4
At 0, the surface temperature of the heating roller 30 is detected, and based on the detection signal, the temperature is controlled by the control means (not shown).

[0019]

Therefore, according to the present invention, the direction of the force that the thermistor 40 receives from the heating roller 30 based on the frictional force due to the rotation of the heating roller 30 passes through the fulcrum position of the holding bracket 37. It is possible to prevent the generation of a gap between the thermistor and the heating roller because the rotation moment does not work. As a result, it is possible to prevent the offset toner adhering to the surface of the fixing roller from accumulating in the gap and forming a toner lump, and soiling the sheet with the toner lump during image fixing.

[Brief description of drawings]

FIG. 1 is an enlarged view around a thermistor pressing position in a fixing device that is an embodiment of the present invention.

FIG. 2 is an assembled perspective view of the holding bracket and the fixed bracket.

FIG. 3 is an overall schematic configuration diagram showing an internal mechanism of a laser printer including the fixing device.

FIG. 4 is an enlarged view around a thermistor pressing position in a conventional fixing device.

FIG. 5 is an assembled perspective view of the holding bracket and the fixed bracket.

FIG. 6 is an explanatory diagram illustrating that a gap is created between a rotating heating roller and a thermistor in the fixing device.

[Explanation of symbols]

 23 Fixing device 37 Holding bracket 37b Projection (fulcrum) 40 Thermistor 42 Energizing member Is Thermistor pushing position (2) The tangent line of the heating roller at the thermistor pushing position

Claims (1)

[Claims] 1. The thermistor is held by a holding bracket,
In the fixing device of the electrophotographic apparatus, which biases the holding bracket by urging it by the biasing member to rotate it about the fulcrum and presses the thermistor against the heating roller to detect the surface temperature thereof, pressing the thermistor. The heating roll at this position
A fixing device for an electrophotographic apparatus, in which a fulcrum of the holding bracket is provided substantially on the tangent line of the la.